The present invention relates to organic reagents and their use as catalysts for a variety of reactions. More particularly, this invention relates to the use of an acid addition salt of an imidazolidinone to catalyze various bond-forming reactions. The invention finds utility in the fields of organic synthesis and stereospecific catalysis.
Ancillary (or xe2x80x9cspectatorxe2x80x9d) ligand-metal coordination complexes (e.g. organometallic complexes) and compositions are useful as catalysts, stoichiometric reagents and therapeutic agents. The ancillary ligand contains functional groups that bind to one or more metal centers and remain associated therewith, providing an opportunity to modify the steric, electronic and chemical properties of the active sites of the complex, i.e., the metal centers.
Unfortunately, many organometallic reagents are expensive and depending on their catalytic activity may be not be commercially viable. Generally, organometallic catalysts require bidentate or polydentate ligands that are difficult to synthesize, requiring multiple reaction steps and increased cost. Due to their high sensitivity to oxygen, air and moisture, organometallic catalysts require the use of inert, nonaerobic conditions, both during synthesis and during catalysis and, once catalysis is complete, these catalysts are also problematic as they are difficult to recycle and are generally environmentally unsafe. The inherent toxicity of these compounds greatly reduces their usefulness in pharmaceutical applications. Moreover, many organometallic complexes are useful only for very specific chemical reactions and do not have broad utility as catalysts for a variety of different types of reactions. This problem may be emphasized for the catalysis of reactions leading to chiral molecules, particularly the conversion of either chiral or achiral molecules via enantioselective catalysis to provide a chiral product.
Over the last 30 years enantioselective catalysis has become one of the most important frontiers in exploratory organic synthetic research. In the pharmaceutical industry and other industries, the use of pure enantiomeric molecules is often important for safety and efficacy. Thus, in the production of pharmaceuticals, use of catalysts or reagents that preferentially produce one enantiomer of a molecule relative to another enantiomer is particularly advantageous. Unfortunately, the catalysts that produce such enantiomers are typically organometallic complexes that are specific for a particular reaction. In addition, there is no way to predict with any reasonable accuracy which enantiomer will result. Examples of organometallic catalysts used to prepare chiral materials include BINOL-based complexes (Mikami et al. (1994) J. Am. Chem. Soc. 116:2812; Kobayashi et al. (1994) J. Am. Chem. Soc. 116:4083; Mikami et al. (1989) J. Am. Chem. Soc. 111:1940; Mikami et al. (1994) J. Am. Chem. Soc. 116:4077; Keck et al. (1993) J. Am. Chem. Soc. 115:8467; Keck et al. (1995) J. Am. Chem. Soc. 117:2363), BINAP-based complexes (Miyashita et al. (1980) J. Am. Chem. Soc. 102:7932; Miyashita et al. (1984) Tetrahedron 40:1245; Takaya et al. (1986) J. Org. Chem. 51:629; Takaya et al. (1988) Org. Synth. 67:20; Cai et al. (1995) Tetrahedron Lett.. 36:7991), DUPHOS complexes (Burk et al. (1990) Organometallics 9:2653; Burk et al. (1993) J. Am. Chem. Soc. 115:10125; Burk et al. (1992) J. Am. Chem. Soc. 114:6266; Burk et al. (1995) J. Am. Chem. Soc. 112:9375); salen-based complexes (i.e., organometallic complexes containing the N,Nxe2x80x2-bis(3,5-di-t-butylsalicylidene)-1,2-cyclohexanediamino ligand; see, e.g., Li et al. (1993) J. Am. Chem. Soc. 115:5326, and Evans et al. (1993) Tetrahedron Lett. 34:7027), and bisoxazoline-containing compounds (Evans et al. (1993) J. Am. Chem. Soc. 115:6460; Evans et al. (1997) J. Am. Chem. Soc. 119:7893; Evans et al. (1996) Tetrahedron Lett. 37:7481; Corey et al. (1992) Tetrahedron Lett. 3:6807; Gothelf et al. (1996) J. Org. Chem. 61:346).
Despite the observed need and relatively few, narrow solutions, relatively few asymmetric transformations have been reported which employ organic molecules as reaction catalysts. There is tremendous potential for academic, economic and environmental benefit should versatile, chiral organic catalysts be developed. Only a few researchers have disclosed organic catalysts useful for preparing chiral materials. See, e.g., Asymmetric Catalysis in Organic Synthesis, Noyori, R., Ed. (New York: Wiley, 1994) and Asymmetric Synthesis, Ojima, I., Ed. (New York: VCH, 1993), and references cited therein. Also see Yang et al. (1998) J. Am. Chem. Soc. 120(24):5943-5952, who disclose the use of a dioxirane to catalyze enantioselective epoxidation, Shi et al. (1995) J. Chem. Research (S):46-47 (J. Chem. Research (M): 0401-0411), who disclose preparation of chiral quaternary ammonium salts stated to be useful as chiral phase-transfer catalysts by reaction of (R)-(+)-2,2xe2x80x2-bis(bromomethyl)-6,6xe2x80x2-dinitrobiphenyl and (R)-(+)-2,2xe2x80x2-bis(bromomethyl)-1,1xe2x80x2-binaphthyl with cyclic amines such as pyrrolidine, piperidine and 4-hydroxypiperidine. International Patent Publication No. WO 92/02505 to Castelijns also discloses use of a secondary amine in a catalytic transformation, i.e., in conversion of an unsaturated imine to a pyridine product, by reaction with an aldehyde or ketone.
The aforementioned organic catalysts are not, however, useful in catalyzing a broad range of chemical transformations, but are specific for a particular reaction and thus have limited utility. There is accordingly a need in the art for organic catalysts that are versatile with respect to the types of reactions that can be catalyzed, are inexpensive to synthesize, and are readily capable of scale-up for commercialization. It is also desirable that such catalysts be capable of preparing chiral products from starting materials that may be either chiral or achiral in nature.
Accordingly, it is a primary object of the invention to address the aforementioned need in the art and provide methods, catalyst compositions and reaction systems for chemically transforming a substrate, wherein the catalyst composition is nonmetallic, useful for catalyzing a wide variety of reactions and reaction types, relatively inexpensive to synthesize, and simple and straightforward to work with and scale up. Importantly, the catalyst composition may also contain a chiral non-racemic component that enables enantioselective catalysis and synthesis of a chiral non-racemic product.
It is another object of the invention to provide a process for transforming a compound containing a functional group to provide a product in which the functional group contains at least one newly formed covalent bond, wherein the transformation is carried out in the presence of a catalyst composition comprising an acid addition salt of an imidazolidinone.
It is yet another object of the invention to provide a chemical reaction wherein an nonmetallic, organic catalyst composition as provided herein lowers the LUMO (lowest unoccupied molecular orbital) of a substrate to facilitate reaction thereof.
It is a further object of the invention to provide such processes and reactions wherein the catalyst composition contains a chiral component.
It is still a further object of the invention to provide novel compounds, useful as catalyst compositions, in the form of acid addition salts of an imidazolidinone.
It is still an additional object of the invention to provide a reaction system composed of the aforementioned catalyst composition and a substrate such as an xcex1,xcex2-unsaturated carbonyl compound.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention.
In one aspect, then, the invention is directed to an imidazolidone salt having the structure of formulae (IV) or (IV-A) 
wherein:
R5, R6 and R7 are independently selected from the group consisting of hydroxyl, sulfhydryl, amino, substituted amino, carboxyl, hydrocarbyl (e.g., alkyl, alkenyl, alkynyl, aryl, alkaryl, alkaryl, etc.), substituted hydrocarbyl (e.g., substituted alkyl, alkenyl, alkynyl, aryl, alkaryl, alkaryl, etc.), heteroatom-containing hydrocarbyl (e.g., heteroatom-containing alkyl, alkenyl, alkynyl, aryl, alkaryl, alkaryl, etc.), and substituted heteroatom-containing hydrocarbyl (e.g., substituted heteroatom-containing alkyl, alkenyl, alkynyl, aryl, alkaryl, alkaryl, etc.);
the substituents R8 and R9 may be hydrido or halo, or they may be selected from the aforementioned substituent possibilities given for R5, R6 and R7, and any two or more of R5, R6, R7, R8 and R9 can be linked to form a cyclic group, typically through a hydrocarbylene, substituted hydrocarbylene, heteroatom-containing hydrocarbylene or substituted heteroatom- containing hydrocarbylene linkage;
the subscript xe2x80x9cnxe2x80x9d is 0 or 1;
the substituent R10 is a cyclic group, either substituted or unsubstituted; and
the Bronsted acid HX, which provides the anion Xxe2x88x92, may be selected from any number of substituted aromatic alcohols, organic acids, inorganic acids and combinations thereof, generally although not necessarily having a pKa of less than about 5.
In another aspect, the invention involves use of the aforementioned imidazolidinone salt as a catalyst composition. For example, compounds of formulae (IV) or (IV-A) can be used to catalyze the reaction of a first reactant containing a functional group having a xcfx80 bond or an equivalent thereof (e.g., a xcex4 bond having xcfx80 bond-type reactivity, as in cyclopropyl moieties) with a second reactant. It is believed that by virtue of the interaction between the catalyst composition and the first reactant, the LUMO of the functional group of the first reactant is lowered relative to its initial state (i.e., prior to contact with the catalyst composition) and generally relative to the HOMO (highest occupied molecular orbital) of the second reactant as well. This LUMO-lowering in turn facilitates reaction of the functional group with the second reactant, enabling transformation of the first reactant by formation of new covalent bonds between the LUMO-lowered functional group and a second reactant (in either an intra- or intermolecular reaction). Suitable first reactants include, for example, xcex1,xcex2-unsaturated carbonyl compounds such as xcex1,xcex2-unsaturated ketones and xcex1,xcex2-unsaturated aldehydes.
In some embodiments, the salt maybe mixed with an excess of imidazolidinone to optimize catalytic activity or other aspects of the reaction that is being catalyzed.
As indicated in formulae (IV) and (IV-A), the imidazolidinone salt can be a chiral compound, i.e., the imidazolidinone component of the salt is chiral with respect to an axis, plane or center of asymmetry. Chiral imidazolidinones may be designed to provide high enantioselectivity, such that a desired enantiomer can be synthesized in enantiomerically pure form.